Polycarbonates have been used in a wide variety of applications requiring high performance thermoplastic materials. Although polycarbonates consisting essentially of chemically combined units of the formula, ##STR1## has been satisfactorily molded at temperatures exceeding 250.degree. C., or injection molded to plastic foams at temperatures exceeding 300.degree. C. using particular blowing agents, the use of such polycarbonates, or the employment of additional blowing agents has been somewhat restricted due to the high temperature polycarbonate shaping requirements. It is also known, for example, that polycarbonate consisting essentially of chemically combined units of formula (1) has a glass transition temperature of 150.degree. C. while the corresponding polycarbonate derived from ortho,para-bisphenol-A has a glass transition temperature of 142.degree. C. Continued efforts have been made by the organic thermoplastics industry to improve the flow characteristics of polycarbonates and other organic thermoplastics having chemically combined isopropylidene bisphenol units.